1. Field of the Invention
This invention relates broadly to sealed high voltage tube applications such as neutron generator tubes, X-ray tubes and photomultiplier tubes where high voltage electrodes are present, charged particles flow, and high voltage electrodes must be maintained at well-defined voltage levels relative to each other. This invention has particular application to sealed high voltage tubes useful in the petrophysical arts where the high voltage tubes are constricted to small spaces and are subjected to extreme environments and rough handling, although the invention is not limited thereto.
2. State of the Art
Numerous sealed high voltage tube applications where high voltage electrodes are present and charged particles flow as a current require that the electrodes be at well-defined voltages. Such applications include, but are not limited to, neutron tubes, X-ray tubes and photomultiplier tubes.
There are two common approaches to assign a voltage to an electrode. The most straight-forward approach is to connect the electrode to a power supply. This approach is most often utilized when there are no space constraints affecting how the voltages are generated and applied to the electrodes. A second approach is to define an electrode voltage relative to another electrode by means of a resistance connecting the two electrodes, whereby the electrical current flowing between the two electrodes together with the resistance will define a voltage drop according to Ohm's law. This second approach is typically used in space constrained applications.
Where a resistor is used to define an electrode voltage in sealed high voltage tube applications, the resistor is typically physically connected between the electrodes via welding of the resistor leads to the electrodes. In environments where the sealed tube is part of a system which is subject to shock, vibration, large temperature changes, and other extreme conditions, the welds are prone to failure.